Catalyst composition, method for its production and its use in the production of hydrocarbons from synthesis gas

ABSTRACT

A catalyst composition of use in the production of hydrocarbons from synthesis gas comprises the essential metals 
     (a) at least one of iron, cobalt, nickel and ruthenium, and 
     (b) at least one of lithium, sodium, potassium, calcium and magnesium 
     supported on silicate, as described and claimed in U.S. Pat. No. 4,061,724, the metals [(A)+(b)] being present on the silicalite support in an amount in the range from 0.5 to 15% by weight. The catalyst composition may be modified by addition of the hydrogen form of a crystalline zeolite having the composition expressed as mole ratios of oxides: 
     0.9±0.2M 2  / n  O:W 2  O 3  :20 to 50 YO 2  :zH 2  O 
     wherein M is at least one cation, n is the valence thereof, W is aluminum and/or gallium, Y is silicon and/or germanium and z has a value of 0 to 40, said zeolite being characterized by an XRD pattern which is substantially that of an MFI-type zeolite. Synthesis gas is converted to olefinic hydrocarbons using the unmodified catalyst and to gasoline range hydrocarbons using the modified catalyst.

This is a division of application Ser. No. 512,740, filed July 11, 1983,U.S. Pat. No. 4,542,117.

The present invention relates to a catalyst composition suitable for usein a process for the production of hydrocarbons from snythesis gas, to amethod for its production and to its use as a catalyst in such aprocess.

Recent world events and a forecast longer-term shortage of oil and gashave concentrated attention on the production of gasoline rangehydrocarbons from far more abundant long-term resources, such as fossilfuels, especially coal, which can be converted to a gasoline mixturecomprising carbon monoxide and hydrogen (hereinafter to be referred toas synthesis gas), which in turn can be converted to hydrocarbons. Apractical long-known method for effecting this conversion is theFischer-Tropsch synthesis which employs in its simplest form a supportediron catalyst, though over the years a variety of alternative metals,such as cobalt, ruthenium, nickel and tungsten and a variety ofpromoters, such as thoria, potassium carbonate, potassium oxide andalumina, have been proposed. The product of such a process consists of abroad spectrum of hydrocarbons between C₁ and C₃₀ and is mainly composedof linear paraffins. The use of such a product for fuels and chemicalsfeedstocks requires lengthy and expensive separation procedures.

More recently, a new class of synthesis gas conversion catalystscomprising a carbon monoxide reduction catalyst combined with a ZSM-5type zeolite developed by Mobil has been reported. It has beendemonstrated that gasoline can be produced in a yield of over 60% oftotal hydrocarbon, constituting essentially 100% of the liquid product,by combining an iron Fischer-Tropsch catalyst with an excess volume of aZSM-5 type zeolite. In a further development, the replacement of iron insuch a catalyst by ruthenium was reported. Replacement of the ZSM-5 typezeolite by silicalite, a form of silica developed by Union Carbidehaving a similar structure to that of ZSM-5 zeolite, impregnated withiron and promoted by potassium is reported to have an exceptionally highselectivity for the production of C₂ -C₄ olefins from synthesis gas.

We have now developed a catalyst composition having a high selectivityin the conversion of synthesis gas to hydrocarbons and in a modificationthereof to gasoline range hydrocarbons, in particular aromatichydrocarbons.

Accordingly, the present invention provides a catalyst compositionsuitable for use in a process for the production of hydrocarbons fromsynthesis gas which composition comprises the essential metals:

(a) at least one of iron, cobalt, nickel and ruthenium, and

(b) at least one of lithium, sodium, potassium, calcium and magnesiumsupported on silicalite, the metals [(a)+(b)] being present on thesilicalite support in an amount in the range from 0.5 to 15% by weight.

As used throughout this specification, the term "silicalite" means theproduct as described and claimed in U.S. Pat. No. 4,061,724.

Silicalite, is a silica polymorph, which after calcination in air at600° C. for one hour has a mean refractive index of 1.39±0.01, aspecific gravity at 25° C. of 1.70±0.05 g/cc and an X-ray powderdiffraction pattern in which the six strongest d-values are those setforth in Table A hereinafter.

                  TABLE A                                                         ______________________________________                                        d-A                Relative Intensity                                         11.1 + 0.2         VS                                                         10.0 + 0.2         VS                                                         3.85 + 0.07        VS                                                         3.82 + 0.07        S                                                          3.76 + 0.05        S                                                          3.72 + 0.05        S                                                          ______________________________________                                    

Silicalite may suitably be prepared by the hydrothermal crystallisationof a reaction mixture comprising water, a source of silica and analkylonium compound at a pH of 10 to 14 to form a hydrous crystallineprecursor, and subsequently calcining that precursor to decomposealkylonium moieties present therein. Further details of this process maybe found in the aforesaid U.S. Pat. No. 4,061,724. The use of silicasources contaminated with alumina may lead to the incorporation of verysmall amounts of alumina into the silicalite, either within theframework structure and/or within the pores and/or on the surface of thecrystals. It is desirable that the amount of alumina, especially thatincorporated in the crystal lattice, be kept to a minimum. Becausesilicalite is essentially free of alumina it is substantially non-acidicand cannot be cation-exchanged.

In addition to the essential metals (a) and (b), there may also bepresent one or more of the metals thorium, zirconium and manganese (c).

A suitable catalyst composition comprises the metals iron, ruthenium andpotassium supported on silicalite.

The active form of the catalyst is thought to comprise the essentialmetals in their metallic form, though it is possible that certain of themetals may be present in other forms, such as for example the oxides.Thus, whilst the elemental metals may be deposited on the silicalitesupport in metallic form, they are preferably deposited on the supportin the form of reduceable compounds thereof and thereafter reduced.

The metals (a) and (c) may suitably be deposited on the silicalitesupport by impregnation with either aqueous or non-aqueous solutions ofsuitable reduceable compounds, eg the carbonyls, of the metals. Suitablenon-aqueous solvents for the metal compounds include benzene, heptane,toluene and tetrahydrofuran. The metal (b) may suitably be deposited onthe silicalite support by impregnation with an aqueous solution of asoluble compound of the metal, eg a hydroxide or a salt. Suitably thesilicalite support may be impregnated first with an aqueous solution ofa compound of the metal (b) and then with a non-aqueous solution ofcompounds of the metals (a) and and optionally (c). Alternatively, themetals (a) and optionally (c) may be added as separate solutions.Suitably, the silicalite after impregnation with the aqueous solution ofthe compound of the metal (b) may be dried and calcined, suitably at atemperature in the range of 400° to 600° C., before furtherimpregnation. The order of addition of the metals (a), (b) and (c) maybe changed if so desired. Other methods conventionally used fordepositing metals on supports, such as by precipitation from solutionsof their salts, may be employed. The metal (a) may suitably be iron andruthenium and the metal (c) may suitably be potassium. The ratio of (a)to (b) to (c) may vary over a wide range. After depositing the metals(a), optionally (b), and (c) in compound form on the silicalite, it ispreferred to heat the silicalite in a reducing atmosphere, for examplein a stream of a reducing gas. Typically this may be effected by heatingthe silicalite with the metals deposited thereon at a temperature in therange of 200° to 450° C. in a stream of hydrogen for a period of from 1to 72 hours.

The catalyst according to the invention comprising the essential metals(a) and (b) and the optional metal(s) (c) supported on silicalite isactive for the conversion of synthesis gas selectively to olefinichydrocarbons.

Accordingly, in another aspect the present invention provides a processfor the conversion of synthesis gas to olefinic hydrocarbons whichprocess comprises contacting the synthesis gas under conditions ofelevated temperature with a catalyst as hereinbefore described.

Methods for preparing synthesis gas are well known in the art andusually involve the partial oxidation of a carbonaceous substance, egcoal. Alternatively, synthesis gas may be prepared, for example, by thecatalytic steam reforming of methane. Although it is preferred to usesubstantially pure synthesis gas, the presence of such impurities ascarbon dioxide and nitrogen can be tolerated. On the other hand,impurities which have a deleterious effect on the reaction should beavoided. The ratio of hydrogen to carbon monoxide in the synthesis gasmay vary widely. Normally, the molar ratio of hydrogen to carbonmonoxide may be in the range from 10:1 to 1:10, preferably from 5:1 to1:5. Methods for adjusting the molar ratio of hydrogen to carbonmonoxide by the so-called shift reaction are well known in the art.

The synthesis gas may suitably be contacted with the catalyst at anelevated temperature in the range 200° to 450° C., preferably from 225°to 375° C. The pressure may suitably be in the range from atmospheric to100 bars.

The process may be operated batchwise or continuously, preferablycontinuously. The contact time, defined as: ##EQU1## may suitably be inthe range from 1 to 30 seconds, preferably from 1 to 10 seconds.

The catalyst may suitably be employed in the form of either a fixed bed,a fluidised bed or a moving bed.

Use of the catalyst of the present invention in the process for theproduction of olefins can lead to a high selectivity to lower olefins,for example ethylene, propylene and butylenes.

The catalyst composition according to the invention may suitably bemodified by combination with the hydrogen form of a crystalline zeolitehaving the composition expressed as mole ratios of oxides:

0.9±0.2 M₂ /_(n) O:W₂ O₃ :20 to 50 YO₂.zH₂ O

wherein M is at least one cation, n is the valence thereof, W isaluminum and/or gallium, Y is silicon and/or germanium and z has a valueof 0 to 40, said zeolite being characterised by an XRD pattern which issubstantially that of an MFI-type zeolite.

Preferably W is aluminium and Y is silicon.

The ratio of the silicalite supported portion to the hydrogen form ofthe crystalline zeolite portion of the modified catalyst may suitably bein the range from 10:1 to 1:10.

A preferred catalyst composition comprises the metals iron, rutheniumand potassium supported on silicalite and the hydrogen form of anMFI-type crystalline aluminosilicate.

MFI-type zeolites are defined in the Atlas of Zeolite Structure Types byW. M. Meier and D. J. Olson, published by the Structure Commission ofthe International Zeolite Association, 1978, in terms of their crystalstructure as determined by reference to an XRD diffraction pattern.

Zeolite ZSM-5, as described and claimed in U.S. Pat. No. 3,702,886(Mobil) has a composition and an XRD powder diffraction patternconforming with that specified for the crystalline zeolite, which in itshydrogen ion-exchanged form constitutes the second component of thecomposition. Zeolite ZSM-5 may suitably be prepared by hydrothermalcrystallisation of an aqueous mixture containing tetrapropyl ammoniumhydroxide, sodium oxide, an oxide of aluminium or gallium, an oxide ofsilica or germanium and water, as described in the aforesaid U.S. Pat.No. 3,702,886. Alternatively, ZSM-5 may be prepared by the methodsdescribed in the complete specifications of U.K. Pat. Nos. 1,365,318 and1,471,440 (Mobil) and 1,553,209 (ICI). Crystalline zeolites having theaforesaid chemical composition and XRD pattern may also be prepared byhydrothermal crystallisation of a mixture containing a source of alkalimetal, a source of silica, a source of alumina, water and either asource of ammonium ions as described in our European patent publicationNo. 30811, or either a di- or trialkanolamine as described in ourEuropean patent publication No. 2900, or either monoethanolamine ormonopropanolamine as described in European patent publication No. 2899.The aforesaid publications are only illustrative of the methods by whichthe desired crystalline zeolites may be prepared and are not in any wayintended to be restrictive.

Whichever method is used to prepare the crystalline zeolite, the cationM in the as-synthesised form will invariably be an alkali metal and isusually sodium. It may be converted to the active hydrogen form byion-exchange. Suitably ion-exchange may be effected either with anaqueous solution of an acid, for example a mineral acid, such ashydrochloric acid, or with an aqueous solution of an ammonium salt toform the ammonium-exchanged form, followed by decomposition of theammonium-exchanged form. Such techniques are conventionally employed inthe art.

It is particularly preferred to produce the modified catalyticcomposition for use in the process of the invention by mixing thatportion of the catalyst comprising the metals (a) and (b) and optionally(c) supported on silicalite with the ammonium ion-exchanged form of thecrystalline zeolite of defined composition and XRD pattern and, aftermixing, decomposing the ammonium ion-exchanged form of the crystallinezeolite to produce the hydrogen form.

As mentioned hereinbefore, the modified catalyst composition of thepresent invention is active for the conversion of synthesis gas togasoline range hydrocarbons and in particular to aromatic hydrocarbons.

According to another aspect of the present invention there is provided aprocess for the production of gasoline range hydrocarbons from synthesisgas which process comprises contacting synthesis gas at elevatedtemperature and either atmospheric or elevated pressure with a catalystcomprising the modified catalyst composition as hereinbefore described.

Although it is preferred to use substantially pure synthesis gas, thepresence of such impurities as carbon dioxide and nitrogen can betolerated. On the other hand, impurities which have a deleterious effecton the reaction should be avoided. The ratio of hydrogen to carbonmonoxide in the synthesis gas may vary widely. Normally the molar ratioof hydrogen to carbon monoxide may be in the range from 5:1 to 1:5.

The elevated temperature may suitably be in the range from 200° to 550°C. and the pressure may suitably be in the range from 0 to 100 bars.

The process may be operated batchwise or continuously, preferablycontinuously. The contact time, defined as: ##EQU2## may suitably be inthe range from 1 to 30 seconds.

The catalyst may suitably be employed in the form of either a fixed bed,a fluidised bed or a moving bed. Before use in the reaction thecomposition is preferably activated by heating in a reducing atmosphere,for example in a stream of a reducing gas. Typically this may beeffected by heating the catalyst at a temperature in the range from 200°to 450° C. in a stream of hydrogen for a period of from 1 to 72 hours.

The invention will now be particularly described by reference to thefollowing Examples.

EXAMPLE 1 Preparation of [Ru₀.₂₄ Fe₀.₃ K₀.₁₃ Silicalite₆.₈ ][H-MFI]Composition Using Non-Aqueous Solvent

Silicalite (6.8 g) was impregnated with potassium hydroxide (0.18 g) inwater (6 ml). The mixture was dried on a steam bath for 2 hours and thencalcined at 440° C. in a slow stream of air for 4 hours.

Fe₃ (CO)₁₂ (0.9 g) dissolved in tetrahydrofuran (40 ml) was added to thesilicalite/KOH in six multiple incipient wetness impregnations, (6-8 ml)each time with vacuum drying between impregnations. The final vacuumdrying was carried out at 100° C.

Ru₃ (CO)₁₂ (0.5 g) dissolved in tetrahydrofuran (60 ml) was impregnatedon to the silicalite/KOH/Fe₃ (CO)₁₂ mixture using a similar technique asfor the iron impregnation.

The K/Fe/Ru impregnated silicalite was transferred to a furnace tube andheated under a slow flow of hydrogen at 120° C. for 2 hours. Thereduction was then carried out as follows: 20 min at 220° C., 2 hours at300° C., then cooled, all under a slow flow of hydrogen.

The impregnated silicalite (6.8 g) was mixed with MFI zeolite having asilica to alumina molar ratio of 33.7:1 (ammonia form) (7.0 g) and thenpressed into small pellets. The pellets were heated at 400° C. in astream of air for 4 hours, cooled and then sieved to 8-20 mesh. Thecatalyst was reduced at 208° C. under a slow flow of hydrogen for 72hours before use.

EXAMPLE 2 Use of catalyst in the conversion of synthesis gas tohydrocarbons

Synthesis gas was passed over a bed of the [Ru₀.₂₄ Fe₀.₃ K₀.₁₃Silicalite₆.₈ ][H-MFI] composition prepared as described in Example 1under the following conditions and with the following results:

    ______________________________________                                        Conditions                                                                    ______________________________________                                        Run pressure           =     20 bars                                          Run temperature        =     450° C.                                   Catalyst               =     15 ml                                            Feed gas CO:H.sub.2 molar ratio                                                                      =     1:1                                              Contact time           =     1.64 sec                                         ______________________________________                                    

Under these reaction conditions 53.5% of the carbon monoxide fed wasconverted and an organic liquid product with the following composition(% w/w) was isolated:

    ______________________________________                                        C.sub.5 -C.sub.8 straight chain paraffins                                                             =     17.0                                            Benzene                 =     9.7                                             Toluene                 =     28.2                                            Ethyl benzene           =     4.3                                             Xylenes                 =     17.2                                            C.sub.9 to C.sub.11 aromatics                                                                         =     23.6                                            ______________________________________                                    

The main reaction products were methane and carbon dioxide.

EXAMPLE 3 Preparation of [Ru₀.₂₄ Fe₀.₃ K₀.₁₃ SILICALITE₆.₈ ] catalystusing water as solvent

To a solution of ruthenium trichloride (3.36 g) in hot deionised water(50 ml) was added a solution of iron (III) nitrate (13.02 g) in hotdeionised water (50 ml) followed by a solution of potassium hydroxide(2.16 g) in deionised water (50 ml). The solution was then added tosilicalite (40.92 g) and the mixture shaken for 1 minute. The slurry wasdried on a rotary evaporator under high vacuum, by slowly raising thetemperature to 70° C. The catalyst was then heat treated in air at 120°C. for 16 hours and then reduced as follows: 2.0 hours at 125° C., 2.0hours at 225° C. and 2.0 hours at 320° C., then cooled all under a slowflow of hydrogen.

EXAMPLE 4 Use of catalyst of Example 3 in the conversion of synthesisgas to olefinic hydrocarbons

Synthesis gas was passed over a bed of a portion of the catalystobtained in Example 3 under the following conditions and with thefollowing results:

    ______________________________________                                        Conditions:                                                                   ______________________________________                                        Pressure =             20 bars                                                Temperature =          325° C.                                         Period of Run =        6.0 hours                                              Feed CO/H.sub.2 molar ratio =                                                                        1:1                                                    Contact time =         5.02 seconds                                           Catalyst =             15 ml                                                  Product Selectivity %                                                         Ethylene               8.0                                                    Ethane                 5.0                                                    Propene                16.0                                                   Propane                2.0                                                    Butene                 2.0                                                    Overall Conversion     26%                                                    ______________________________________                                    

EXAMPLE 5

Example 4 was repeated under the following conditions and with thefollowing results:

    ______________________________________                                        Conditions:                                                                   ______________________________________                                        Pressure =             20 bars                                                Temperature =          380° C.                                         Period of Run =        2.0 hours                                              Feed CO/H.sub.2 molar ratio =                                                                        1:1                                                    Contact time =         2.54 seconds                                           Catalyst =             15 ml                                                  Product Selectivity %                                                         Ethylene               8.0                                                    Ethane                 6.0                                                    Propene                16.0                                                   Propane                2.0                                                    Butene                 1.0                                                    Overall Conversion     32%                                                    ______________________________________                                    

Comparison Test 1

A catalyst consisting of 3.03% w/w ruthenium supported on silicalite wasprepared using an abbreviated form of the procedure described in Example3.

Synthesis gas was passed over a bed of the catalyst under the followingconditions and with the following results:

    ______________________________________                                        Conditions:                                                                   ______________________________________                                        Pressure =             30 bars                                                Temperature =          410° C.                                         Period of Run =        6 hours                                                Feed CO/H.sub.2 molar ratio =                                                                        1:1                                                    Contact time =         0.56 seconds                                           Catalyst =             6 ml                                                   Product Selectivity %                                                         Ethylene               1.0                                                    Ethane                 11.08                                                  Propene                9.06                                                   Propane                12.06                                                  Overall Conversion     47.57%                                                 ______________________________________                                    

Comparative Test 2

A catalyst consisting of 15% w/w iron supported on silicalite wasprepared using an abbreviated form of the procedure described in Example3.

Synthesis gas was passed over a bed of the catalyst under the followingconditions and with the following results:

    ______________________________________                                        Conditions:                                                                   ______________________________________                                        Pressure =             30 bars                                                Temperature            535° C.                                         Period of Run =        1 hour                                                 Feed CO/H.sub.2 molar Ratio =                                                                        1:1                                                    Contact time =         0.53 seconds                                           Catalyst =             6 ml                                                   Product Selectivity %                                                         Ethylene                0.8                                                   Ethane                 10.22                                                  Propene                 3.98                                                  Propane                10.93                                                  C.sub.4                 8.36                                                  Overall Conversion     75.37%                                                 ______________________________________                                    

EXAMPLE 6 Preparation of [Ru₀.₂₄ Fe₀.₃ K₀.₁₃ SILICALITE]₁.₃ [H-MFI]catalyst

A further portion of the impregnated silicalite (8 g) obtained inExample 3 was mixed with the ammonium ion-exchanged form of an MFIzeolite (6.0 g) having a silica to alumina molar ratio of 33.7:1 andpressed into small pellets. The pellets were heated at 400° C. in astream of air for 4 hours, cooled and sieved to 8-20 B.S.S. mesh. Thecatalyst was reduced at 225° C. under a slow flow of hydrogen for 18hours.

EXAMPLE 7 Use of the catalyst of Example 6 in the conversion ofsynthesis gas to hydrocarbons

Synthesis gas was passed over a bed of the catalyst obtained in Example6 under the following conditions and with the following result:

    ______________________________________                                        Conditions:                                                                   ______________________________________                                        Run Pressure =         20 bars                                                Run Temperature =      394° C.                                         Catalyst =             15 ml                                                  Feed CO/H.sub.2 molar ratio =                                                                        1:1                                                    Contact time =         6.39 seconds                                           ______________________________________                                    

Results

Under these reaction conditions 53.6% of the carbon monoxide fed wasconverted and an organic liquid product with the following composition(% w/w) was isolated.

    ______________________________________                                        C.sub.5 -C.sub.8 straight chain paraffins                                                          23.1                                                     Benzene              4.1                                                      Toluene              17.3                                                     Xylenes              21.0                                                     Ethyl Benzene        4.0                                                      C.sub.9 -C.sub.11 aromatics                                                                        30.5                                                     ______________________________________                                    

We claim:
 1. A process for the production of aromatic hydrocarbons fromsynthesis gas which process comprises contacting synthesis gas atelevated temperature and either atmospheric or elevated pressure withacatalyst composition which comprises the essential metals:(a) rutheniumand at least one of iron, cobalt and nickel, and (b) at least one oflithium, sodium, potassium, calcium and magnesium supported onsilicalite the metals [(a)+(b)] being present on the silicalite supportin an amount in the range from 0.5 to 15% by weight, modified bycombination with the hydrogen form of a crystalline zeolite having thecomposition expressed as mole ratios of oxides:
 0. 9±0.2M_(2/n) O:W₂ O₃:20 to 50 YO₂ :zH₂ O (I)wherein M is at least one cation, n is thevalence thereof, W is aluminium, or gallium, Y is silicon and/orgermanium and z has a value of 0 to 40, said zeolite being characterisedby an XRD pattern which is substantially that of an MFI-type zeolite. 2.A process according to claim 1 wherein in the formula (I) W is aluminiumand Y is silicon.
 3. A process according to claim 1 wherein the ratio ofthe silicalite supported portion of the catalyst composition to thehydrogen form of the crystalline zeolite portion is in the range from10:1 to 1:10.
 4. A process according to claim 1 wherein the essentialmetals are ruthenium, iron and potassium.
 5. A process according toclaim 1 wherein the crystalline zeolite is ZSM-5.
 6. A process accordingto claim 1 wherein the catalyst combination is obtained by mixing thatportion of the catalyst comprising the metals (a) and (b) supported onsilicalite with the ammonium ion-exchanged form of the crystallinezeolite and, after mixing, decomposing the ammonium ion-exchanged formof the crystalline zeolite to produce the hydrogen form.
 7. A processaccording to claim 10 wherein the elevated temperature is in the rangefrom 200° to 550° C.
 8. A process according to claim 1 wherein thepressure is in the range from 0 to 100 bars.